Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
Earnings per Share
Effect, participating securities			$ 0.0
Basic and Diluted EPS:
Income from continuing operations	$ 14.4	$ 20.1	0.5	$ 37.2
Less income attributable to participating shares	(0.1)	(0.1)		(0.2)
Income from continuing operations attributable to common stockholders	14.3	20.0	0.5	37.0
Loss from discontinued operations attributable to common stockholders	(6.2)	(5.9)	(6.8)	(18.6)
Net income (loss) attributable to common stockholders for earnings per share	$ 8.1	$ 14.1	$ (6.3)	$ 18.4
Weighted Average Shares:
Weighted average common shares outstanding - basic	34,900,000	34,600,000	34,900,000	34,600,000
Additional shares from the assumed exercise of stock options	100,000	400,000	100,000	400,000
Weighted average common shares outstanding - diluted	35,000,000.0	35,000,000.0	35,000,000.0	35,000,000.0
Earnings (Loss) per share - basic:
Earnings from continuing operations	$ 0.41	$ 0.58	$ 0.01	$ 1.07
Loss from discontinued operations	(0.18)	(0.17)	(0.20)	(0.54)
Earnings (Loss) per share - basic	0.23	0.41	(0.19)	0.53
Earnings (Loss) per share - diluted:
Earnings from continuing operations	0.41	0.57	0.01	1.06
Loss from discontinued operations	(0.18)	(0.17)	(0.19)	(0.53)
Earnings (Loss) per share - diluted	$ 0.23	$ 0.40	$ (0.18)	$ 0.53
Antidilutive shares excluded from the computation of diluted earnings per share (in shares)	1,743,000	267,000	1,743,000	267,000